The progressive senator Elizabeth Warren accused Donald Trump of firing a prominent prosecutor to install “cronies” , warning on Sunday of “a massive fight” in the Senate over his picks for new US attorneys.

On Saturday, Trump fired Preet Bharara, the US attorney of the southern district of Manhattan, where the prosecutor had pursued corruption cases against members of both the Republican and Democratic parties. In November, Bharara met with Trump and his nominee for attorney general, Jeff Sessions, and said he had “agreed to stay on” after conversations with both.

But on Friday afternoon, Sessions abruptly ordered 46 prosecutors, nearly all appointees of Barack Obama, to resign “effective immediately”. Bharara refused to resign and was fired, saying in a brief public statement: “One hallmark of justice is absolute independence, and that was my touchstone every day that I served.”

New presidents typically replace the appointees named by their predecessors, but not since 1993 has a new administration done so in such a rapid, sweeping fashion. And late Saturday, an official speaking on condition of anonymity told the Associated Press that the sudden dismissal of Bharara was preceded by an unusual phone call from the White House to the prosecutor’s office.

On Thursday, the president’s secretary called Bharara, who declined to take the call because the justice department has strict rules about communications between presidents and prosecutors. Bharara told Trump’s secretary he could not speak directly with the president.

The White House has declined to comment on why Trump fired Bharara after asking him to continue in his role. Warren seized on this ambiguity, tweeting on Sunday that Trump “talked a big game about getting corruption out of gov[ernment]. But he wants a bunch of tame prosecutors who won’t investigate him.”

“Preet Bharara had authority over Trump Tower,” she wrote, noting the US attorney’s jurisdiction over Manhattan, the Bronx and Westchester, New York. Trump “called him directly, breaching protocol”, Warren continued. “24 [hours] later he was asked to resign.”

“More GOP & Dems respect Preet Bharara as a fearless prosecutor who stands up to both parties & Wall Street. I guess that’s why Trump fired him,” she said, before drawing a comparison to Trump’s decision to fire Sally Yates. The president fired Yates, who was acting attorney general in the first weeks of his administration, after she refused to defend his executive order limiting travel, and after she warned Trump that his national security adviser had misled the White House about conversations with Russia’s ambassador.

Warren said the president “wants people like AG Sessions, a loyalist who lied to the Senate about meeting with the Russians”, alluding to Session’s failure, under oath, to disclose his own conversations with the ambassador.

“The Senate confirms US Attorneys. And you’re not replacing real prosecutors with cronies [with]out a massive fight,” she added.

At the time of his dismissal, Bharara was overseeing separate investigations into the staffs of New York mayor Bill de Blasio and New York governor Andrew Cuomo, both leading critics of the Trump administration. His office had also opened an investigation into Fox News over a possible failure to inform shareholders of multimillion-dollar settlements with female employees who had accused Roger Ailes, the former CEO, of sexual harassment.

Over his seven years as US attorney for the southern district, Bharara prosecuted high-profile cases on financial hacking and insider trading and against JPMorgan Chase, Toyota and the billionaire investor Steven Cohen, earning the prosecutor the nickname “the sheriff of Wall Street”.